memoryd: the day and the month of a time with get, never a slice

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/memoryd/src/journal.rs

@@ -84,11 +84,7 @@ pub(crate) fn append(store: &Store, mut record: Record, now: Timestamp) -> Resul
     //    `serde_json::to_string(&record)`, then `store.append(&format!("edits/{month}.jsonl"),
     //    &format!("{line}\n"))?` where month is the first 7 characters of day. Ok(record.id).
     let rfc = now.to_rfc3339();
-    let day = if rfc.len() >= 10 {
-        &rfc[..10]
-    } else {
-        "0000-00-00"
-    };
+    let day = rfc.get(..10).unwrap_or("0000-00-00");
     let taken = records(store)?
         .iter()
         .filter(|r| r.id.starts_with(&format!("{day}-")))
@@ -97,7 +93,7 @@ pub(crate) fn append(store: &Store, mut record: Record, now: Timestamp) -> Resul
     let edits_dir = store.path("edits");
     std::fs::create_dir_all(&edits_dir).map_err(|e| format!("{}: {e}", edits_dir.display()))?;
     let line = serde_json::to_string(&record).map_err(|e| e.to_string())?;
-    let month = &day[..7];
+    let month = day.get(..7).unwrap_or("0000-00");
     store.append(&format!("edits/{month}.jsonl"), &format!("{line}\n"))?;
     Ok(record.id)
 }

crates/memoryd/src/notes.rs

@@ -34,8 +34,7 @@ pub struct Note {
 /// A time as the notes show it: to the minute, in UTC.
 pub fn minute(time: Timestamp) -> String {
     let s = time.to_rfc3339();
-    let head = if s.len() >= 16 { &s[..16] } else { &s };
-    format!("{head}Z")
+    format!("{}Z", s.get(..16).unwrap_or(&s))
 }
 
 fn class_name(class: DataClass) -> &'static str {

crates/memoryd/src/recall.rs

@@ -158,7 +158,7 @@ pub fn recall(
         Some(fts) => search(index, &fts, args.k)?,
     };
     let rfc = now.to_rfc3339();
-    let month = &rfc[..7];
+    let month = rfc.get(..7).unwrap_or("0000-00");
     std::fs::create_dir_all(store.path("recalls")).map_err(|e| format!("recalls: {e}"))?;
     let logged = Logged {
         time: rfc.clone(),

crates/memoryd/src/review.rs

@@ -100,7 +100,7 @@ pub fn submit(
     //    accepted")).
     args.check()?;
     let rfc = ctx.now.to_rfc3339();
-    let day = &rfc[..10];
+    let day = rfc.get(..10).unwrap_or("0000-00-00");
     let taken = waiting(store)?
         .iter()
         .filter(|line| match line {